Essentials: Breathing for Mental & Physical Health & Performance | Dr. Jack Feldman

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now for my conversation with Dr. Jack Feldman. Thanks for joining me today.

**Jack Feldman** (0:21)
Pleasure to be here, Andrew.

**Andrew Huberman** (0:23)
You're my go-to source for all things respiration and how the brain and breathing interact. You're the person I call. Why don't we start off by just talking about what's involved in generating breath?

**Jack Feldman** (0:36)
So on the mechanical side, which is obvious to everyone, we want to have AF flow in, inhale, and we need to have AF flow out. And the reason we need to do this is because for body metabolism, we need oxygen.
And when oxygen is utilized through the aerobic metabolic process, we produce carbon dioxide. And so we have to get rid of the carbon dioxide that we produce, in particular because the carbon dioxide affects the acid-base balance of the blood, the pH. And all living cells are very sensitive to what the pH value is. So your body is very interested in regulating that pH. So how do we generate this AF flow? We have to expand the lungs. And as the lungs expand, basically it's like a balloon that you would pull apart, the pressure inside that balloon drops, and air will flow into the balloon. That lowers the pressure in the air sacs called alveoli, and air will flow in because pressure outside the body is higher than pressure inside the body when you're doing this expansion, when you're inhaling. What produces that? Well, the principal muscle is the diaphragm, which is sitting inside the body just below the lung, and when you want to inhale, you basically contract the diaphragm and it pulls it down. And as it pulls it down, it's inserting pressure forces on the lung, the lung wants to expand. At the same time, the rib cage is going to rotate up and out, and therefore expanding the dark cavity, the thoracic cavity. At the end of inspiration, under normal conditions, when you're at rest, you just relax. And it's like pulling on a spring. You pull down a spring and you let go and it relaxes. Where does that activity originate? The region in the brain stem, that's once again this region sort of above the spinal cord, which was critical for generating this rhythm. It's called the pre-Butzinger complex. This small site, which contains in humans, a few thousand neurons, it's located on either side and works in tandem. And every breath begins with neurons in this region beginning to be active. And those neurons then connect ultimately to these motor neurons going to the diaphragm and to the external intercostals, causing them to be active and causing this inspiratory effort. When the neurons in the pre-buttock complex finish their burst of activity, then inspiration stops and then you begin to exhale because of this passive recall of the lung and rib cage.

**Andrew Huberman** (3:25)
Is there anything known about the activation of the diaphragm and the intercostal muscles between the ribs as it relates to nose versus mouth breathing?

**Jack Feldman** (3:37)
I don't think we fully have the answer to that. Clearly there are differences between nasal and mouth breathing. At rest, the tendency is to do nasal breathing because the air flows that are necessary for normal breathing is easily managed by passing through the nasal cavities. However, when your ventilation needs to increase, like during exercise, you need to move more air, you do that through your mouth because the airways are much larger than and therefore you can move much more air. But at the level of the intercostals and the diaphragm, their contraction is almost agnostic to whether or not the nose and mouth are open.

**Andrew Huberman** (4:23)
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